With significant developments in laser technology and its application to ophthalmology, laser surgery has become the technique of choice for ophthalmic procedures, such as refractive surgery for correcting myopia, hyperopia, astigmatism, and so on, and cataract surgery for treating and/or removing a cataractic lens. Laser eye surgery generally uses different types of laser beams, such as ultraviolet lasers, infrared lasers, and near infrared, ultra-short pulsed lasers, for various procedures and indications.
A surgical laser beam is preferred over manual tools like microkeratomes because it can be focused precisely on extremely small amounts of ocular tissue, thereby enhancing accuracy and reliability. For example, in the commonly-known LASIK (Laser Assisted In Situ Keratomileusis) procedure, an ultra-short pulsed laser is used to cut a corneal flap to expose the corneal stroma for photoablation with an excimer laser. Ultra-short pulsed lasers emit radiation with pulse durations as short as 10 femtoseconds and as long as 3 nanoseconds, and a wavelength between 300 nm and 3000 nm. Besides cutting corneal flaps, ultra-short pulsed lasers are used to perform cataract-related surgical procedures, including capsulorhexis, capsulotomy, as well as softening and/or breaking of the cataractous lens. Examples of laser systems that provide ultra-short pulsed laser beams include the Abbott Medical Optics iFS™ Advanced Femtosecond Laser and the IntraLase™ FS Laser,
Conventional ophthalmic surgical laser systems generally include an operator interface used by the system operator to set-up, control, monitor, and direct the laser treatment. For obvious reasons, the laser beam's ability to accurately and precisely incise tissue, as well as its ability to properly determine the incision depth, —(e.g., depth measured from the surface of the cornea, the laser system interface, and/or the laser source)—, are important.
As such, eye biometry information is often taken before surgery to measure the location, depth, and length of all planes of a patient's eye. A system for obtaining ophthalmic biometry data is described in U.S. Pat. No. 7,887,184, issued to Baer et al., which is incorporated here by reference in its entirety. Pre-surgical measurements, however, may not account for how the internal geometry of the eye is affected by an ophthalmic patient interface, which is typically used to restrain eye movement during surgery. Examples of ophthalmic patient interface devices used to stabilize the eye are described in commonly-owned U.S. Pat. No. 6,863,667, issued to Webb et al., U.S. Pat. No. D462,442 issued to Webb, U.S. Pat. No. 6,623,476, issued to Juhasz et al., and co-pending U.S. patent application Ser. No. 13/230,590, which are incorporated here by reference. Furthermore, most pre-surgical measurements generally require a separate or additional device from the surgical system, adding cost. For example, some surgical systems add additional pre-surgery imaging devices, such as an optical coherence tomographer (OCT). Besides adding system costs, additional imaging devices like OCT require regular calibration and maintenance to maintain strong a spatial correlation between the surgical laser and the OCT.
Accordingly, there is a need for improved systems and methods for depth detection during laser ophthalmic surgery.